Determination of the density of gap states: field effect and surface adsorption

✍ Scribed by H. Fritzsche

• Publisher: Elsevier Science
• Year: 1980
• Weight: 514 KB
• Volume: 2
• Category: Article
• ISSN: 0379-6787
• DOI: 10.1016/0379-6787(80)90033-2

✦ Synopsis

Can the conductivity, the thermopower or the photoconductivity of an amorphous silicon film be determined? Does the field effect measure the density of gap states? What is the magnitude of the mobility gap? These questions do not have a simple answer. High quality films contain space charge layers adjacent to the substrate interface and near the top surface. These layers can strongly influence the electronic properties of the film, and changes may occur during the course of measurements as charges are exchanged with adsorbates, with the surface oxide or with traps in the insulating substrate. Other causes for change are light, thermal treatments and high transverse electric fields. Attempts to remove or fix these space charges or at least to understand their origin and effects are discussed. The validity of several assumptions needed for interpreting field effect measurements is questioned.